SQL-DATABASE ERROR

Database error in WoltLab Burning Board (): Link-ID == false, connect failed
mysql error: Can't connect to local MySQL server through socket '/tmp/mysql5.sock' (2)
mysql error number: 2002
mysql version: unknown
php version: 5.3.10-1ubuntu3.26
Date: 17.02.2019 @ 14:40
Script: /forum/wbb2/thread.php?threadid=5847
Referer: